fairy ring

A fairy ring is complete circle or arc of fruiting bodies of fungi,
particularly agarics, which commonly appear in fields and lawns. Each colony
of fungi is derived from a single spore from
which the hyphae grow out in all directions
forming an invisible circular colony that only becomes visible when fruiting
bodies are formed at its periphery. The name is derived from the old superstition
that mushrooms growing in a circle represent the path of dancing fairies.